Detailed explanation of common usage examples of bitset in c++

In C++bitsetis a template class for processing fixed-size bit sequences, providing efficient bit operation functions. Here is a detailed introduction to its key features:

1. Declaration and Initialization

• Header file: Need to include<bitset>。
• statement：bitset<N>Indicates a containingNBinary set of bits (Nis a compile-time constant).

bitset<8> b1;       // Default initialization, all bits are 0bitset<4> b2(5);    // Initialize with integers: 0101bitset<4> b3("1010"); // Initialize with string: 1010bitset<4> b4(b3);   // Copy construction

2. Initialization rules

• Integer initialization: High truncation, low truncation.

bitset<3> b(10);    // 10The binary system is1010 → Truncate to010（The value is2）

• String initialization：
  • Strings can only contain'0'and'1'。
  • By default, from stringLeft end (high position)Start parsing.

bitset<4> b("1010"); // High → Low : 1 0 1 0 → Decimal 10bitset<4> b("101010", 2, 4); // From index2Pick4Bit："1010" → The value is10

3. Common operations

• bit access：

  • []Operator: Accessed through index (from right to left, 0 is the lowest bit).
  • test(pos): Check whether the specified bit is 1, and an exception is thrown out of bounds.

bitset<4> b("1010");
bool bit0 = b[0];   // 0 → lowest positionbool bit3 = b[3];   // 1 → Highest position

• Modify bit：

  • set(pos, val): Set a certain bit (default 1).
  • reset(pos): Clear a bit (set to 0).
  • flip(pos): Flip a certain position.

(0);       // 1010 → 1011
(3);     // 1011 → 0011
(1);      // 0011 → 0001

• Statistics and judgments：

  • count(): Returns the number of 1.
  • any()/none()/all(): Determine whether there is/no/all are 1.

if (()) cout << "At least 1 bit is 1";

4. Bit operation

• support&、|、^、~、<<、>>Equal operator (the length must be the same):

bitset<4> a("1010"), b("1100");
auto c = a & b;     // 1000
auto d = a << 1;    // 0100

5. Type conversion

• to_ulong()/to_ullong(): Convert to an unsigned integer (possibly overflowed).
• to_string(): Convert to a string to specify padding characters.

bitset<4> b(10);
string s = b.to_string(); // "1010"

6. Application scenarios

• Bit flag management: such as permission control, status marking.
• Bitmask operation: Quickly filter or modify specific bits.
• Data compression: efficiently store boolean values.

Sample code

#include <bitset>
#include <iostream>
using namespace std;
int main() {
    bitset<8> b1(42);          // 00101010
    bitset<8> b2("10101010");  // 10101010
    cout << b1 << endl;         // Output 00101010    (0);                 // becomes 00101011    ();                 // becomes 0101010101    cout << (b1 & b2) << endl; // 00000001
    cout << b1.to_ulong() << endl; // 43
    return 0;
}

Things to note

• Visit across the border：test(pos)Will check for cross-border,[]Won't.
• performance:Efficient bit operation, suitable for intensive computing.
• String order: The first character of the string corresponds to the high bit.

bitsetIt is a powerful tool for processing binary data. Combined with clear bit sequence rules and rich interfaces, it can significantly simplify bit-level operation code.

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